A solid oxide fuel cell (SOFC) is an all-solid device that converts the chemical energy of gaseous fuels such as hydrogen and simple hydrocarbons into electricity through electrochemical processes. With the ever-increasing concern over the future availability of alternative energy sources, there is significant interest in the research and development of SOFCs because of their unique advantages over traditional power generation technologies. The efficiency of SOFCs is inherently high because it is not limited by the Carnot efficiency of a heat engine. In SOFCs, hydrogen and simple hydrocarbons can be electrochemically oxidized at the anode. Due to the operating temperature range of SOFCs, the fuel-processor can be incorporated into the fuel cell stack, which enables innovative thermal integration/management design features to provide excellent system efficiencies. SOFCs can be also used for co-generation of steam or hot water, which if coupled with gas turbines to produce electrical power can enhance the overall system efficiency and the range of applications. In addition, the greenhouse gas emissions from SOFCs are much lower than those emitted from conventional power plants.
Current research activities in the development of SOFCs are increasingly focused on reducing operating temperatures of SOFCs from traditional values near 1000° C. to lower temperatures of 500-800° C. Such a reduction in operating temperature would lessen sealing problems, reduce performance degradation, and enable replacement of ceramic interconnects by cheaper metallic materials. However, a reduction of the operating temperature is detrimental from an electrochemical point of view. In general, fuel cells suffer from three major losses including (a) activation losses arising from sluggish kinetics of the electrochemical charge-transfer reactions at the electrodes, (b) ohmic loss mainly stemming from slow ionic conduction in the electrolyte, and (c) concentration loss originating from the limited mass transport at high current densities. At reduced operating temperature, the thermally-activated electrode reactions and ion transport in the electrolyte become slower, resulting in lowered fuel cell performance. To reduce ohmic losses at reduced temperatures, an electrolyte with higher ionic conductivity or a thinner electrolyte structures is required. As the electrolyte resistance decreases, the overall cell losses then become dominated by the polarizations of electrochemical reactions at the anode and cathode. Therefore, the electrode material requires particular attention in the development and optimization of low temperature SOFCs.
Pt is well known for its chemical stability and for its excellent electrical properties at high temperatures, leading to enormous application prospects in catalysis and microelectronics. Pt has been reported to have excellent catalytic activity for the O2 reduction reaction and the H2 oxidation reaction at the electrode/electrolyte interface of an SOFC even at low operating temperatures. When Pt is used as the catalytic material/electrode, the oxygen reduction reaction is dominated by the electrode surface path, and bulk diffusion of oxygen is negligible. Thus, maximizing the surface area (triple phase boundary) while minimizing the Pt bulk is beneficial. Meanwhile, sufficient electrical connectivity is required, putting severe limitations on Pt film thickness by traditional deposition methods.
Though Pt provides excellent catalytic activity for the O2 reduction reaction and the H2 oxidation reaction at the electrode/electrolyte interface of an SOFC at low operating temperatures, pure Pt catalysts suffer from an increase of grain size and a decrease of porosity during fuel cell operation originating from the change of microstructure at high temperature. This effect is aggravated with decreasing Pt film thickness.
What is needed is a method of stabilizing the Pt thin film microstructure at high temperatures, and improving the adhesion of the Pt films onto the electrolyte. What is further needed is a method of reducing the noble metal loading in fuel cells for reducing the cost of fuel cells. Additionally what is needed is a method to modify the chemical properties of the substrate surface for patterning resulting in a Pt electrode/catalyst and Pt current collector grids on the SOFC to improve the fuel cell power efficiency.